Butadiene is highly myelotoxic to mice, but not to rats. The degree of human sensitivity is still uncertain. Butadiene appears to require metabolism to epoxides to exert toxicity. The origin of toxic metabolites could be the liver or the bone marrow. Hepatic metabolism of butadiene has been extensively studied, but bone marrow metabolism has not. We have developed methodology to examine butadiene metabolism in bone marrow or liver tissue. We have extended this methodology to permit the study of stereochemistry of butadiene metabolites, and have developed routes to both unlabelled and radiolabelled enantiomers of butadiene monoxide as well as radiolabelled butadiene itself. We have also completed initial studies of butadiene epoxidation in bone marrow. The proposed studies are designed to examine the hypothesis that genetic differences in stereochemistry of metabolism are important determinants in the observed species sensitivity to butadiene. The proposed studies will first answer questions of stereochemistry of butadiene metabolism in rat and mouse liver. The studies will then be extended bone marrow of rat, mouse and human. The following specific aims will be accomplished. 1. The overall composition of stereoisomers of each butadiene metabolite will be determined upon exposure of rat or mouse liver microsomes or hepatocytes to butadiene. This will determine the profile of compounds available for systemic distribution through the animal. 2. The same studies will be done with exposure of microsomes or hepatocytes to individual enantiomers of butadiene monoxide, a situation modeling initial enantio-selective epoxidation of butadiene. 3. The degree of irreversible metabolite binding to tissue of microsomes and hepatocytes will be determined by incubation with radiolabeled butadiene and enantiomers of butadiene monoxide. 4. The stereochemical preferences of individual metabolic steps in the metabolism of butadiene by rat and mouse liver microsomes or cytosol will be determined by preventing sequential or side reactions. 5. The studies completed in liver will be extended to bone marrow cells of rat, mouse and human. Observed species differences in stereochemistry of butadiene metabolism will provide support for the central hypothesis, and will provide important mechanistic information regarding the choice of models for approximating human toxicity.